The working up of hydrogenation residues by low-temperature carbonization in an indirectly heated low-temperature carbonization drum is described in "Die katalytische Druckhydrierung von Kohlen, Teeren und Mineraloelen [The Catalytic Pressure Hydrogenation of Coals, Tars, and Crudes Oils]," W. Kroenig, Springer Verlag, Berlin/Goettringen/Heidelberg 1950 (see pages 44 ff., 188 ff., and 252). In the processes disclosed in this treatise, the residue containing carbon is pyrolytically decomposed under suitable conditions into low-temperature carbonization gas, low-temperature carbonization oil, and low-temperature carbonization coke. Fine coke dust is removed from the low-temperature carbonization vapors in a low-temperature carbonization drum. The fine coke dust and the nonvolatile components contained in the residue (such as asphaltenes) form agglomerates that lead to clogging of the low-temperature carbonization vapor outlet. Additionally, the removal of the coke dust leads, with the subsequent condensation, in addition to the uncondensed low-temperature carbonization gas, to the development of low-temperature carbonization oil that has a high solid content.
The condensate obtained with the known processes thus contains considerable amounts of solids and unconverted high molecular substances and cannot be considered a valuable product, since it requires a further expensive working up or must be recycled for repeated low-temperature carbonization in the drum before it can be used.